This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-077091 filed on Mar. 17, 2000, the entire content of which is incorporated herein by reference.
The present invention generally relates to an actuator for an oscillator. More particularly, the present invention pertains to an actuator for an oscillator for oscillating an electrostatic driven type oscillator provided with an angular rate sensor.
A block diagram of a known actuator for an oscillator for oscillating electrostatic driven type oscillators provided with angular rate sensors is shown in FIG. 14. As shown in FIG. 14, a signals for the displacement of the electrostatic driven type oscillator caused by the oscillation in a driving direction is outputted from a driving direction displacement detecting electrode 81 to a displacement signal detecting portion 82.
The displacement signal outputted to the displacement signal detecting portion 82 is synchronously detected at a timing synchronized to the displacement in a driving direction in a synchronous detection circuit 83 to be outputted to an amplitude adjuster 84 as oscillation amplitude data.
Simultaneously, the displacement signal outputted to the displacement signal detecting portion 82 is outputted to the amplitude adjuster 84 after being phase-shifted by approximately 90 degrees in a 90 degree phase shifter 85. By means of the phase shift of the displacement signal by approximately 90 degrees via the 90 degree phase shifter 85, an alternating voltage component of the drive signal having phase-contrast by approximately 90 degrees relative to the displacement signal is generated in the amplitude adjuster 84 to facilitate the oscillation of the electrostatic driven type oscillator.
The oscillation amplitude data outputted to the amplitude adjuster 84 is compared with a predetermined amplitude value in the amplitude adjuster 84. When the oscillation amplitude data is smaller than the predetermined amplitude value, the alternating voltage component of the drive signal having increased amplitude is generated (incremental adjustment). On the other hand, when the oscillation amplitude data is larger than the predetermined amplitude value, the alternating voltage component of the drive signal having decreased amplitude is generated (decremental adjustment). The amplitude adjustment of the alternating voltage component of the drive signal in the foregoing manner is performed for controlling the amplitude driving force of the oscillator to have constant amplitude in the driving direction of the oscillator. The alternating voltage component of the drive signal of which the amplitude is adjusted in the foregoing manner is outputted to an adder 86.
In the adder 86, a drive signal is generated by incorporating the alternating voltage component of the drive signal of which the amplitude is adjusted and the direct-current voltage component (bias voltage) of the drive signal having a predetermined value. The drive signal generated in this manner is supplied to a drive electrode 87 fixed on a substrate. When the voltage of the drive electrode of the oscillator side is grounded (GND), the oscillator is oscillated to have constant amplitude in the driving direction by the oscillation of the electrostatic attraction (oscillation driving force) generated to be proportional to the second power of the drive signal (driving voltage) between the oscillator and the drive electrode 87.
Generally, electrostatic driven type oscillators are oscillated by a drive signal consisting of the alternating voltage component and the direct-current voltage component supplied thereto. The electrostatic driven oscillators are oscillated by the oscillation of the electrostatic attraction (oscillation driving force) generated proportional to the second power of the drive signal between the electrostatic driven type oscillator and a drive electrode. The displacement (oscillation amplitude) of the electrostatic driven type oscillator according to the oscillation in the driving direction is detected as the displacement signal. The generation of the drive signal is controlled by an amplitude adjusting means to maintain the constancy of the oscillation amplitude of the electrostatic driven type oscillator in the driving direction based on the detected displacement signal. By controlling the generation of the drive signal, the oscillation driving force (electrostatic attraction) of the electrostatic driven type oscillator is controlled to maintain the constancy of the oscillation amplitude of the electrostatic driven type oscillator in the driving direction.
The alternating voltage component of the drive signal is a cause of the noise of the displacement detecting signal because of the approximately same frequency with the displacement detecting signal. Thus, the alternating voltage component of the drive signal becomes a main cause of the detection error of the oscillation condition of the electrostatic driven type oscillator. When the angular rate is detected while the electrostatic driven type oscillator is oscillated, the alternating voltage component causes a lag of the detected output.
When the amount of the noise deriving from the alternating component of the drive signal is stable, the detection error of the oscillation and the lag of the detected output of the angular rate maintain an approximately fixed level. When the detection error of the oscillation and the lag of the detected output of the angular rate maintain an approximately fixed level, they can be easily corrected. Therefore, when the amount of the noise deriving from the alternating voltage component of the drive signal is stable, it is easy to correct the error. However, when the increase or decrease of the alternating voltage component of the drive signal is adjusted for maintaining the oscillation amplitude in the driving direction to be constant while the Q factor of the electrostatic driven type oscillator in the driving direction is fluctuated by the change of the electrostatic driven type oscillator due to the passage of time and the change of the environmental temperature, the amount of the noise mixed in the displacement detecting signal is fluctuated. Thus, the detecting error of the oscillation condition of the electrostatic driven type oscillator and the lag of the detected output of the angular rate are fluctuated by the increase or decrease of the alternating voltage component of the drive signal.
In light of the foregoing, it is an object of the present invention to provide an actuator for an oscillator preventing unfavorable conditions such as the change of the detection error and the fluctuation of the lag of the detecting output of the angular rate of the oscillation of the electrostatic driven type oscillator by controlling the fluctuation of the amount of the noise mixed in the displacement signal.
It is a further object of the present invention to provide an actuator for oscillators minimizing the fluctuation of the alternating voltage component of the drive signal.
To attain the above objects, the following technical means are provided with the actuator for the oscillator of the present invention which includes an electrostatic driven type oscillator, an oscillator driving means for oscillating the electrostatic driven type oscillator by outputting a drive signal thereto, a displacement detecting means for detecting the displacement based on the oscillation of the electrostatic driven type oscillator as a displacement signal, and an amplitude adjusting means for controlling the generation of the drive signal outputted from the oscillator driving means to maintain the constancy of the oscillation amplitude of the electrostatic driven type oscillator based on the detected displacement signal. The amplitude adjusting means includes an alternating voltage component generating means for generating an alternating voltage component of the drive signal having a constant amplitude or an amplitude proportional to the oscillation amplitude and a direct-current voltage component generating means for generating the direct current of the drive signal controlled to be increased or decreased based on the detected displacement signal. Based on the drive signal consisting of the alternating voltage component and the direct-current voltage component, the oscillation driving force of the electrostatic driven type oscillator is controlled to maintain the constancy of the oscillation amplitude of the electrostatic driven type oscillator.
According to the foregoing technical means, the amplitude adjusting means generates an incorporated drive signal consisting of the alternating voltage component or the alternating voltage component proportional to the oscillation amplitude maintaining a constant amplitude by the alternating voltage component generating means and the direct component generating means and the direct-current voltage component of which increase or decrease is controlled based on the detected displacement signal. Based on the drive signal, the oscillation driving force (electrostatic attraction) of the electrostatic driven type oscillator is controlled to maintain the constancy of the oscillation amplitude of the electrostatic driven type oscillator in the driving direction.
Thus, even when the Q factor of the electrostatic driven type oscillator in the driving direction is fluctuated due to the change of the electrostatic driven type oscillator by the passage of time and the change of the environment temperature, only the direct-current voltage component of the drive signal is increased and decreased to maintain the constancy of the alternating voltage component (amplitude). Accordingly, even when the Q factor of the electrostatic driven type oscillator in the driving direction is fluctuated due to the passage of time and the change of the environment temperature, the amount of the noise in the displacement signal deriving from the alternating voltage component of the drive signal is kept stable. This helps the correction of detection error changes as long as the noise amount is stable by keeping a fixed level.
Another aspect of the technical means of the actuator for the oscillator of the present invention involves the arrangement whereby the increase or decrease of the direct-current voltage component of the drive signal is controlled by one of three ways as follows. The increase or decrease of the direct-current voltage component of the drive signal is controlled to be proportional to the difference between the oscillation amplitude of the electrostatic driven type oscillator detected based on the displacement signal and a predetermined amplitude or is controlled to be proportional to a value obtained by performing time integration of the difference between the oscillation amplitude of the electrostatic driven type oscillator detected based on the displacement signal and the predetermined amplitude or is controlled to be proportional to an addition of the value obtained by performing time integration of the difference between the oscillation amplitude of the electrostatic driven type oscillator detected based on the displacement signal and the predetermined amplitude and the value proportional to the difference between the oscillation amplitude and the predetermined amplitude.
When the increase or decrease of the direct-current voltage component of the drive signal is controlled to be proportional to the difference between the oscillation amplitude of the electrostatic driven type oscillator detected based on the displacement signal and the predetermined amplitude, the lag of the control of the oscillation driving force of the electrostatic driven type oscillator is minimized to provide a control having a good response to the oscillation amplitude of the electrostatic driven type oscillator. When the direct-current voltage component of the drive signal is controlled to be proportional to the value obtained by performing time integration of the difference between the oscillation amplitude of the electrostatic driven type oscillator detected based on the displacement signal and the predetermined amplitude, the difference between the oscillation amplitude of the electrostatic driven type oscillator and the predetermined amplitude is controlled to be almost zero, which can provide a control with high accuracy to the oscillation amplitude of the electrostatic driven type oscillator. When the direct-current voltage component of the drive signal is controlled to be proportional to the addition of the value obtained by performing time integration of the difference between the oscillation amplitude of the electrostatic driven type oscillator detected based on the displacement signal and the predetermined amplitude and the value proportional to the difference between the oscillation amplitude and the predetermined amplitude, the lag of the control of the oscillation driving force of the electrostatic driven type oscillator is minimized and also the difference between the oscillation amplitude of the electrostatic driven type oscillator and the predetermined amplitude is controlled to be almost zero, which can provide a control with high response and high accuracy to the amplitude of the electrostatic driven type oscillator.
A further aspect of the technical means of the present invention involves the arrangement whereby the alternating voltage component of the drive signal is generated having a phase contrast by approximately 90 degrees to the displacement signal and having the amplitude of the alternating voltage component of the drive signal proportional to the amplitude of the displacement signal or is generated proportional to a signal obtained by performing one of the differentiation, the integration, or the 90 degree phase-shift to the displacement signal.
When the alternating voltage component of the drive signal is generated having a phase-contrast of 90 degrees to the displacement signal, the electrostatic driven type oscillator is oscillated at the most effective resonant point. When the amplitude of the alternating voltage component of the drive signal is generated proportional to the amplitude of the displacement signal, provided that the oscillation of the electrostatic driven type oscillator becomes stable, an alternating voltage component of the drive signal having a constant amplitude is generated. Thus, for instance, compared to the conventional method as shown in FIG. 14 which generates the alternating voltage component of the drive signal separately, the structure of the alternating voltage component generating means is simplified. Further, when the alternating voltage component of the drive signal is generated proportional to the signal obtained by performing the differentiation, the integration, or the phase-shift by 90 degrees to the displacement signal, provided that the oscillation of the electrostatic driven oscillator is stable, the alternating voltage component of the drive signal having a constant amplitude is generated only by damping or amplifying the signal obtained by performing the differentiation, the integration or the phase-shift by 90 degrees to the displacement signal based on the oscillation of the oscillator. Thus, for instance, the structure of the alternating voltage component generating means (circuit structure) is simplified compared to the conventional method as shown in FIG. 14 which generates the alternating voltage component of the drive signal separately. By performing the differentiation, the integration, or the phase-shift by 90 degrees to the displacement signal, the alternating voltage component of the drive signal having the phase-contrast by approximately 90 degrees to the displacement signal is generated. Accordingly, the electrostatic driven type oscillator is oscillated, at the most effective resonant point.
A still further aspect of the technical means of the present invention involves a first drive electrode and a second drive electrode having opposite electrostatic attraction directions, which is generated between the electrostatic driven type oscillator and the first and the second drive electrodes respectively. According to the foregoing technical means, the electrostatic driven type oscillator is oscillated by respective signals, each having an inverted alternating voltage component with respect to each other supplied to the first and the second drive electrodes in which the directions of the electrostatic attraction respectively generated between the electrostatic driven type oscillator are opposed to one another. In this case, the noise mixed with the displacement signal deriving from the alternating voltage component of each drive signal applied to the first and the second drive electrodes is offset. This reduces the total noise deriving from the alternating voltage component.
Furthermore, by providing a structure equalizing the electrostatic attraction of the first drive electrode and the second drive electrode generated between the electrostatic driven type oscillator by respective drive signals including an inverted alternating voltage component, the component of the force generated proportional to the second power of the direct-current voltage component and the component of the force generated proportional to the second power of the alternating voltage component in the oscillation driving force (electrostatic attraction) applied to the electrostatic driven type oscillator are offset from one another to reduce unnecessary motion.